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offshore units, such as semisubmersibles. The oil is periodically offloaded to

shuttle tankers.

FPSO systems may also be used as the primary production facilities to

develop marginal oil fields or fields in remote deep-water areas without the need of

a pipeline infrastructure.

Ship-shaped offshore units have various benefits when compared to other

types of floating structures in terms of ample work area, deck load, high storage

capability, structural strength, shorter lead time, building/capital cost, and

suitability for conversion and reusability. However, similar to other types of

floating platforms, their displaced volume below the water line is comparatively

large, and the response and failures of the structures under harsh environmental

conditions associated with waves, winds, and currents are significant issues to

consider in design and operation.
Dynamic/impact-pressure actions arising from green water, sloshing, and

slamming are also issues to be resolved both in design and for operation,
particularly in harsh weather areas.

Careful consideration of an adequate station-keeping system and adequate
design considerations of systems, such as the riser system, are necessary in order to

avoid difficulties due to vessel motions. The riser system used for ship-shaped

offshore units is usually flexible (rather than rigid). There are several methods of

mooring the ship-shaped structures, including turret moorings, articulated towers,

and soft yoke systems, which permit the unit to weathervane, that is, rotate

according to the direction of external forces. Thrusters can assist the mooring

system to reduce forces and motions.

In relatively benign environmental areas, FPSO systems may be spread-

moored; also, rigid risers may be acceptable. However, in harsh environmental

areas – for example, with revolving tropical storms such as typhoons in the South

China Sea

and tropical cyclones offshore of Northwestern Australia – careful consideration is
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